Epothilones A and B are highly active anticancer compounds isolated from the Myxobacteria of the genus Sorangium. The full structures of these compounds, arising from an x-ray crystallographic analysis were determined by Höfle. G. Höfle et al., Angew. Chem. Int. Ed. Engl., 1996, 35, 1567. The total synthesis of the epothilones is an important goal for several reasons. Taxol is already a useful resource in chemotherapy against ovarian and breast cancer and its range of clinical applicability is expanding. G. I. Georg et al., Taxane Anticancer Agents; American Cancer Society: San Diego, 1995. The mechanism of the cytotoxic action of taxol, at least at the in vitro level, involves stabilization of microtubule assemblies. P. B. Schiff et al., Nature (London), 1979, 277, 665. A series of complementary in vitro investigations with the epothilones indicated that they share the mechanistic theme of the taxoids, possibly down to the binding sites to their protein target. D. M. Bollag et al., Cancer Res., 1995, 55, 2325. Moreover, the epothilones surpass taxol in terms of cytotoxicity and far surpass it in terms of in vitro efficacy against drug resistant cells. Since multiple drug resistance (MDR) is one of the serious limitations of taxol (L. M. Landino and T. L. MacDonald in The Chemistry and Pharmacology of Taxol and its Derivatives, V. Farin, Ed., Elsevier: New York, 1995, ch. 7, p. 301), any agent which promises relief from this problem merits serious attention. Furthermore, formulating the epothilones for clinical use is more straightforward than taxol.
Accordingly, the present inventors undertook the total synthesis of the epothilones, and as a result, have developed efficient processes for synthesizing epothilones A and B, the corresponding desoxyepothilones, as well as analogues thereof. The present invention also provides novel intermediates useful in the synthesis of epothilones A and B and analogues thereof, compositions derived from such epothilones and analogues, purified compounds of epothilones A and B, and desoxyepothilones A and B, in addition to methods of use of the epothilone analogues in the treatment of cancer. Unexpectedly, certain epothilones have been found to be effective not only in reversing multi-drug resistance in cancer cells, both in vitro and in vivo, but have been determined to be active as collateral sensitive agents, which are more cytotoxic towards MDR cells than normal cells, and as synergistic agents, which are more active in combination with other cytotoxic agents, such as vinblastin, than the individual drugs would be alone at the same concentrations. Remarkably, the desoxyepothilones of the invention have exceptionally high specificity as tumor cytotoxic agents in vivo, more effective and less toxic to normal cells than the principal chemotherapeutics currently in use, including taxol, vinblastin, adriamycin and camptothecin.